1. Technical Field
The present invention relates to a gas analysis device and a gas analysis method that analyze a plurality of gaseous components contained in a gas.
2. Related Art
Biogenic gases such as human exhaled gases, skin gases and rectum gases (flatulence) contain several hundred sort of types of gaseous substances such as volatile organic compounds (VOCs). They include substances that have causal relationships with diseases, and such knowledge has been increasingly applied to biogenic gas diagnoses that diagnose diseases by quantitatively analyzing these substances as markers. Therefore, researches for identifying VOCs correlated with diseases, and research and development for new measurement/analysis methods have been vigorously performed.
As one of approaches to simple and rapid measurement of trace amounts of components in a biogenic gas, there is absorption spectrometry that utilizes a mid-IR laser. In order to detect a known VOCs correlated with diseases, this approach determines the component concentration by absorption spectroscopic measurement by using, as a light source, a narrow band mid-IR laser whose wavelength is caused to match the absorption spectrum of the component. For example, the quantity of nitrogen monoxide (NO) in a biogenic gas that enables distinction between asthma and chronic coughing can be determined by a quantum cascade laser with a wavelength of 5.27 μm (1898 cm−1), and a detection lower limit of approximately 1 ppb has been realized. Also, acetaldehyde that is originated from lung cancer can be measured with a detection lower limit of 80 ppb by utilizing a quantum cascade laser of 5.79 μm (1727 cm−1).
The VOCs correlated with diseases, and their infrared absorption spectrums are shown in FIG. 4. The characteristic absorption bands of functional groups such as aldehyde, ketone, carboxylic acid and amide that are important as biogenic products concentrate around 1600 to 1800 cm−1, and a number of the characteristic absorption spectra unique to molecules are distributed in a region around 800 to 1400 cm−1 which region is also called a finger-print region of molecules.
Currently, the effective wavelength tuning region of a mid-IR laser whose spectrum width is narrowed is very narrow at several cm−1, and it has been becoming difficult to perform simultaneous measurement of a plurality of gases. To cope with this, development of an analysis device for a plurality of gaseous components contained in a gas that utilizes a light source having a narrow spectrum and a wide wavelength tuning region in the mid-IR region has been anticipated.
Patent Document 1 proposes a method in which: a multiplexed beam formed by combining a near-IR pump beam and a near-IR signal beam from a semiconductor laser for detecting a first gas medium is caused to enter PPLN crystal to generate a near-IR or mid-infrared difference frequency light for detecting a second gas medium; from the multiplexed beam formed by combining the signal beam, the difference frequency light and the pump beam that has passed a multi-pass cell enclosing a sample gas, only the signal beam and the difference frequency light are separated onto the same optical axis; then the signal beam and difference frequency light are caused to enter a MCT detector to detect them simultaneously; and concentrations of the first gas medium and the second gas medium are analyzed based on electrical signals from the MCT detector.